Polycrystalline diamond (PCD) materials known in the art are formed from diamond grains or crystals and a ductile metal binder and are synthesized by high temperature/high pressure processes. Such material is well known for its mechanical properties of wear resistance, making it a popular material choice for use in such industrial applications as cutting tools for machining, and subterranean mining and drilling where such mechanical properties are highly desired. For example, conventional PCD can be provided in the form of surface coatings on, e.g., inserts used with cutting and drilling tools, to impart improved wear resistance thereto.
Traditionally, PCD inserts used in such applications are formed by coating a carbide substrate with one layer of PCD and one or two transition layers. Such inserts comprise a substrate, a surface layer, and often a transition layer to improve the bonding between the exposed layer and the support layer. The substrate is, most preferably, a carbide substrate, e.g., cemented carbide, tungsten carbide (WC) cemented with cobalt (WC—Co).
The coated layer or layers of PCD conventionally may comprise a metal binder up to about 30 percent by weight to facilitate diamond intercrystalline bonding and bonding of the layers to each other and to the underlying substrate. Metals employed as the binder are often selected from cobalt, iron, or nickel and/or mixtures or alloys thereof and can include metals such as manganese, tantalum, chromium and/or mixtures or alloys thereof. However, while higher metal binder content typically increases the toughness of the resulting PCD material, higher metal content also decreases the PCD material hardness, thus limiting the flexibility of being able to provide PCD coatings having desired levels of both hardness and toughness. Additionally, when variables are selected to increase the hardness of the PCD material, typically brittleness also increases, thereby reducing the toughness of the PCD material.
Generally, such conventional PCD materials exhibit extremely high hardness, high modulus, and high compressive strength, and provide a high degree of wear protection to a cutting or drilling element. However, in more complex wear environments known to cause impact and fretting fatigue, layers formed from conventional PCD can fail by gross chipping and spalling. For example, drilling inserts coated with a thick PCD monolayer may exhibit brittleness that causes substantial problems in practical applications. Conventional methods of improving the performance of PCD layers include optimizing grain size and controlling cobalt content to increase toughness, but the effect of these methods is limited.
Cemented tungsten carbide (WC—Co), on the other hand, is a cermet material that is well known for its mechanical properties of hardness, toughness and wear resistance, making it a popular material of choice for use in such industrial applications as subterranean mining and drilling. Cermet materials refer to materials that contain both a ceramic and a metallic element. Popular cermet materials includes those comprising hard grains formed from a carbide, boride, nitride, or carbonitride compound that includes a refractory metal such as W, Ti, Mo, Nb, V, Hf, Ta, Cr, and that comprises a further metallic cementing or binding agent. Cemented tungsten carbide is a well known cermet. Because of the above-described desired properties, cemented tungsten carbide has been the dominant material used, inter alia, in cutting tool applications for machining, and in subterranean drilling applications such as hard facing, wear inserts, and cutting inserts in rotary cone rock bits, and substrate bodies for drag bit shear cutters.
The mechanical properties associated with cemented tungsten carbide and other cermets, especially the unique combination of hardness toughness and wear resistance, make these materials more desirable than either metals or ceramics alone. Compared to PCD, WC—Co is known to display significantly higher fracture toughness and chipping resistance. However, WC—Co has less wear resistance and hardness than PCD.
U.S. Pat. No. 4,525,178 discloses a composite material comprising a PCD body having cemented carbide pieces disposed therein formed by combining individual diamond crystals with pieces of precemented carbide. The so-formed PCD composite provides improved properties of impact resistance when compared to pure PCD materials, i.e., PCD materials that do not include cemented carbide. However, cutting substrates and/or working surfaces formed from such PCD composite are still known to chip and suffer other types of impact related material failures when exposed to aggressive cutting and/or drilling applications.
U.S. Pat. No. 5,370,195 discloses drill bit inserts comprising a PCD outer layer, an outer transition layer disposed onto an insert substrate, and an inner transition layer interposed between the outer transition layer and the PCD outer layer. The PCD outer layer comprises a minor volume percent of metal and a trace amount of WC or other ceramic additives. The inner and outer transition layers are essentially diamond-carbide composites. Each comprises diamond crystals (i.e., not PCD), particles of tungsten carbide, cobalt, and titanium carbonitride in different volume percentages. Although this diamond-carbide composite does provide some degree of improved impact resistance when compared to a pure PCD material, cutting substrates and/or working surfaces formed from this diamond-carbide composite are known to have greatly reduced wear resistance as compared to PCD. The transition layers are still likely to chip and suffer other types of impact related failures when exposed to aggressive cutting and/or drilling applications.
It is, therefore, desirable that a composite material be constructed that provides desired PCD properties of hardness and wear resistance with improved properties of fracture toughness and chipping resistance, as compared to conventional PCD materials, for use in aggressive cutting and/or drilling applications. It is desired that such composite material display such improved properties without adversely impacting the inherent PCD property of wear resistance. It is desired that such composite material be adapted for use in such applications as cutting tools, roller cone bits, percussion or hammer bits, drag bits and other mining, construction and machine applications, where properties of improved fracture toughness is desired.